Electrical discharge apparatus



NOV. 1937. J. H. JONKER ET AL 2,093,807

ELECTRICAL DISCHARGE APPARATUS Filed March 22, 1932 Fig i i j lhvehtors:

Johan LH. Jonker, Karel Tn.\ an Gessel,

Their Attorney.

Patented Nov. 9, 1937 ELECTRICAL DISCHARGE APPARATUS Johan Lodewyk Hendrik Jonker and Karel I Marinus Van Gessel, Eindhoven, Netherlands,

assignors'to Radio Corporation ofAmerica, a I corporation of Delaware Application March 22, 1932, Serial No. 600,456 In the Netherlands March 24, 1931 1 Claim.

The present invention relates to electrical discharge apparatus, more especially to tubes employing indirectly heated cathodes.

In cathodes of the indirectly heated type, the heater usually consists of a U- or V-shaped filament. The dimensions of the filament, i. e. the gage and length are predetermined in order to provide the proper resistance so that the heat generated by the current will be sufficient for electron emission purposes. In the fabrication of tubes provided with cathodes of this sort, the cathode is heated to a high temperature and the tube pumped so as to deprive the metal of the cathode of gas held by occlusion; this temperature ordinarily is higher than the operating temperature for which the cathode is designed. Under these conditions, the current passing through the heater is greater than normal and tends to render the filament brittle, which may be due to re-crystallization of the metal. The

heater is apt to rupture or burn through at this time or if it survives, the operating life of the tube is considerably shortened and its resistance to breakage due to shocks greatly reduced.

An object of the present invention is to provide an indirectly heated cathode which is adapted not only to ordinary operating or working conditions but also to manufacturing conditions. In both cases, the cathode must operate efficiently. The object is attained in brief, by providing a pair of heater filaments, one of which is designed to operate at the evacuation or manufacturing temperature and the other at the ordinary working temperature. Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing in which Fig. 1 is an elevational view of a tube containing a cathode improved in accordance with the present invention, with several of the electrodes shown in cross-section, while Fig. 2 is a cross-sectional view of a modified form of cathode.

In Fig. 1, numeral I designates an evacuated envelope which may contain gas or vapor, if desired. The envelope terminates in an inverted stem or press 2 which supports the electrodes. The latter comprises a cylindrical anode 3, a helical grid 4 and an indirectly heated cathode 5 held in position at the bottom by a rigid rod 6 fused in the press, and at the top, by a rod 1 secured to a glass arbor 8. This construction and arrangement are well known in the art and need no elaboration. Leading-in conductors 9 are provided for the various electrodes, including the cathode.

The improved cathode consists of a cylindrical member 5 of a suitable metal, such as nickel, closed at the top and open at the bottom. The cathode may be coated with electronically active material, such as alkaline earth oxide. Within the cathode cylinder, there are-two or more filamentary heaters I 0, ll of tungsten or other refractory metal joined at one end to a common leading-in conductor and at the other end to individual leading-in conductors.

The filaments are of substantially the same shape but as will be noted, one is longer. They are arranged, one withinthe other as shown, so as to be mutually independent, physically and electrically. One of the filaments is designed in accordance with well-known calculations, to carry the current necessary for heating the cathode during the gas denudation process and the other is adapted to heat the cathode during the regular operating period. Consequently, when the evacuation of the tube, including the electrodes, has been completed by the usual heating methods, the heater, designed to carry the ordinary operating current, is employed during the life of the tube. However, it will be understood that if desired, both heaters may be employed together, during either the manufacturing or the operating period or both, although ordinarily, the heaters are used separatelyand in a discriminate manner.

Hence, in accordance with our invention, the heater most suited for the particular work at hand is employed, which feature lends enhanced efficiency of operation to the tube, as well as longer life. The extra filament necessitates only a small addition by way of structure and in quantity production increases the cost of manufacture by a very few per cent which is offset by the resulting reduced tube shrinkage.

In Fig. 2, there is shown a modified form of heater H2 in which the filament takes the form of an M or .a double inverted V. The two parts of the heater may be arranged side by side and the apexes brought out to separate leading-in conductors, as shown. One-half of the heater may be used for gas denudation purposes during manufacture of the tube and the other half for operating purposes, each being designed eflicient- 1y to perform its individual function.

While we have shown two typical embodiments of the improved heater, in various arrangement, our invention is not limited thereto as obviously, as many heaters as desired may be employed in any suitable combination during the manufacturing and operating stages; furthermore, the heaters may take any number of shapes and arrangements within the cathode enclosure.

What we claim as new and'desire tosecure by LettersPatent of the United States, is:

An electric discharge device comprising an'envelope containing a cylindrical anode, a helical grid and an indirectly heated cathode of cylindrical configuration, a plurality of heaters withw in the cathode cylinder and the space between said heaters and the cylinder being substantially free of insulating material, one of said heaters of said heaters being arranged within another 10 heater.

J OHAN LODEWYK HENDRIK JONICER. KAREL MARINUS VAN GESSEL. 

